The concept of Geosynthetic Cellular Systems (GCS) has recently emerged as a new method in construction of breakwaters
and coastal protective structures. The method potentially has significant advantages compared to conventional systems from
the standpoint of constructability, cost effectiveness, and environmental considerations. This paper presents the results of
physical model testing on the hydraulic responses of GCS structures under wave action. A series of model tests were carried
out in a wave flume on GCS models with different shapes and soil types, subjected to various wave characteristics. Horizontal
wave forces acting on the models were measured at different elevations. The maximum horizontal force in each test was
calculated and compared with conventional formula of predicting wave pressure on breakwaters. The results show that Goda’s
equation overestimates the hydrodynamic water pressure on these structures. This can be attributed to the influence of seeping
water through the GCS models because of relative permeability of the GCS.